1. Field of the Invention
Exemplary embodiments of the present invention relate to a method and an apparatus for decoding an audio signal; and, more particularly, to a method and an apparatus for decoding an audio signal encoded by a layered sinusoidal pulse coding scheme using one or more sinusoidal pulses.
2. Description of Related Art
As the data transmission bandwidth increases with the development of communication technology, users' demand for high-quality communication services increases. A coding scheme capable of effectively compressing (encoding) and decompressing (decoding) voice/audio signals is necessary to provide high-quality voice/audio communication services.
Communication services have been developed focusing on narrowband codecs, but an interest in wideband codecs is also increasing due to the widespread use of VoIP. Recently, extensive research is being conducted on an extension codec technology that uses a single codec to process narrowband (NB, 300˜3,400 Hz) signals, wideband (WB, 50˜7,000 Hz) signals, and super-wideband (SWB, 50-14,000 Hz) signals. An ITU-T G.729.1 codec is a typical wideband extension codec based on a G.729 narrowband codec. The ITU-T G.729.1 wideband extension codec provides a bitstream-level compatibility with the G.729 narrowband codec at 8 kbit/s, and provides narrowband signals of improved quality at 12 kbit/s. Also, the ITU-T G.729.1 wideband extension codec encodes wideband signals with a bit-rate extensibility of 2 kbit/s from 14 kbit/s to 32 kbit/s, and improves the quality of an output signal with an increase in the bit rate.
Such an extension codec generally uses a layered coding structure in order to provide bandwidth and bit-rate extensibility. The layered coding structure may use different coding schemes according to frequency bands. In general, an upper layer uses a frequency-domain coding scheme in order to increase the throughput of non-voice signals. MDCT is mainly used as a frequency-domain transform scheme, and gain-shape VQ, AVQ, and sinusoidal pulse coding algorithms are used in an MDCT coefficient coding scheme.